Should I gap to my owners manual spec or are they designed to work with the smaller pre-gap they came with?

Harley Davidson recommends 0.40" gap. As to "You should never gap an iridium plug", NGK's website states for Harley Davidson, these should be gapped at 0.40". I've found many websites stating that if re-gap is needed use care not to damage the electrode or the porcelain center. So, it's not that you should not re-gap, it's that you should be extremely careful.

Is this 6r12, if so why does it not say so ?

Because these plugs are IX DCPR7EIX 99 TO 16 HARLEY-DAVIDSON

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NGK Iridium IX DCPR7EIX Spark Plugs Compatible with 1999-2016 Harley Davidson Twin Cam (Pair)

NGK Iridium IX DCPR7EIX Spark Plugs Compatible with 1999-2016 Harley Davidson Twin Cam (Pair)

Product ID: 12508559

Details

Brand
NGK
Core Material
Nickel
Number of Items
2
Top Material Type
Metal
Vehicle Service Type
Motorcycle

⚡Up to 3HP power boost

🔧Pre-gapped for instant install

🛡️Enhanced anti-corrosion metal shell

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Description

⚡ Ignite your ride with NGK’s ultimate spark plug upgrade!

POWER SURGE READY - Unlock up to 3 extra horsepower with cutting-edge iridium tech.
PRECISION PRE GAPPED - Skip the hassle—ready to install right out of the box for a perfect fit.
ULTRA SLIM ELECTRODE - 25% smaller iridium tip means less voltage needed and longer ignition life.
TRUSTED INDUSTRY LEADER - NGK’s top-rated spark plugs keep your Harley roaring with 4.7-star reliability.
CORROSION RESISTANT ARMOR - New metal shell plating guards against rust and wear for lasting durability.

NGK Iridium IX DCPR7EIX spark plugs deliver superior ignition performance for 1999-2016 Harley Davidson Twin Cam models. Featuring a 25% smaller iridium electrode, pre-gapped precision, and enhanced anti-corrosion plating, these plugs boost horsepower by up to 3HP while extending ignition system life. Trusted by thousands with a 4.7-star rating, they offer a hassle-free upgrade for riders seeking peak engine efficiency and durability.

Specifications

ASIN	B003BUCNNS
Automotive Fit Type	Vehicle Specific Fit
Best Sellers Rank	#2,974 in Automotive ( See Top 100 in Automotive ) #9 in Automotive Replacement Spark Plugs
Brand Name	NGK
Compatible with Vehicle Type	Motorcycle
Core Material	Nickel
Customer Reviews	4.7 4.7 out of 5 stars (4,945)
Included Components	NGK DCPR7EIX
Item Type Name	SPARK_PLUG
Item Weight	1.44 ounces
Manufacturer	NGK
Manufacturer Part Number	DCPR7EIX
Manufacturer Warranty Description	Manufacturer Warranty
Model Number	DCPR7EIX
Top Material Type	Metal
UPC	700155016542
Unit Count	2.0 Count

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¥7372

Duties & taxes included

In stock

Sold byAmazon JapanDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to Japan.

Secure transaction

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TrustScore 4.5 | 7,300+ reviews

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